Some vehicle engine systems utilize both direct in-cylinder fuel injection and port fuel injection. The fuel delivery system may include multiple fuel pumps for providing fuel pressure to the fuel injectors. As one example, a fuel delivery system may include a lower pressure fuel pump (or lift pump) and a higher pressure (or direct injection) fuel pump arranged between the fuel tank and fuel injectors. Engine systems with both port and direct fuel injection are becoming increasingly popular, as the benefits of both injection systems may aid in enhancing engine performance. The high pressure fuel pump may be coupled to the direct injection system upstream of a fuel rail to raise a pressure of the fuel delivered to the engine cylinders through the direct injectors. A solenoid activated inlet check valve, or spill valve, may be coupled upstream of the high pressure pump to regulate fuel flow into the pump compression chamber. The spill valve is commonly electronically controlled by a controller which may be part of the control system for the engine of the vehicle. Furthermore, the controller may also have a sensory input from a sensor, such as an angular position sensor, that allows the controller to command activation of the spill valve in synchronism with a driving cam that powers the high pressure pump.
However, engine systems that utilize both port and direct fuel injection may be more expensive and complicated than either of the individual fuel systems. As direct injection systems require additional components and costly modifications to otherwise port-only injection systems, combining the two fuel systems may be too large of a cost for widespread use. As such, cost reductions of combined port and direct fuel injection systems are needed in order to increase the production of such systems. Since the high pressure fuel pump may be required for direct fuel injection, various approaches have been developed to modify the high pressure pump and related systems in order to simplify and/or reduce the cost of the port and direct fuel injection engines, in particular the direct injection system.
In one approach to reduce cost of direct injection fuel systems, shown by Hornby and Humblot in US 2013/0061830, a high pressure (direct injection) fuel pump is modified to deliver fuel under a single pressure to a fuel rail. This approach includes a mechanical flow control valve and a housing that is coupled to the inlet end of the pump. The flow control valve includes a control plunger that controls the valve opening, selectively trapping fuel to be compressed and sent through a pump outlet or pushing fuel out of a compression chamber of the high pressure pump and into the low pressure inlet side of the pump. Opening and closing of the plunger is actuated by fuel on the outlet side of the pump that is channeled to the control valve via ports. From this, the mechanical flow control valve operates on pressure differences between the outlet and inlet of the pump, thereby replacing the solenoid (electronic) valve by providing fuel at one pressure to the fuel rail.
However, the inventors herein have identified potential issues with the approach of US 2013/0061830. First, the addition of features such as the mechanical control valve and ports for communication between the outlet and a low pressure side volume are modifications to the high pressure pump. As such, for implementation of the single pressure fuel system, if multiple high pressure pumps were tested, then each would need to be retrofitted to reflect the changes as described in US 2013/0061830. Also, changes to the high pressure pump may be more difficult than modifying other features in the fuel system, such as the low and high pressures lines. Furthermore, the modified high pressure pump, as it is described, may only provide a single pressure to the fuel rail coupled to the high pressure pump. The inventors do not provide further explanation for providing more than one pressure to the fuel rail. In common systems as previously mentioned, the solenoid activated inlet check valve may be energized to regulate fuel flow through the high pressure pump. Since the solenoid activated inlet check valve is electronically controlled, a continuously-variable amount of fuel may be provided to the pump compression chamber, and as such, a continuously variable pressure may be provided to the fuel rail, or a large number of discrete pressures. Reducing the possible number of fuel rail pressures from a large number to a single pressure may not be conducive with fuel systems that require more than one fuel rail pressure. Finally, the modified high pressure pump involves a number of components along with the plunger that work in unison in order for the pump to operate as desired. If one of the multiple components, such as the spring, pin, valve blade, and valve disk, were to fail, then the function of the high pressure pump may be altered or disabled entirely.
Thus in one example, the above issues may be at least partially addressed by a method, comprising: during a first high pressure fuel pump operating mode, regulating a first fuel rail pressure via a first pressure relief valve; and during a second high pressure fuel pump operating mode, regulating a second fuel rail pressure via a second pressure relief valve, the second pressure relief valve in parallel with the first pressure relief valve and separated by a solenoid valve to direct fuel backflow to either the first or second pressure relief valve. In this way, mechanical pressure regulation of the high pressure pump may be achieved with the addition of several components external to the high pressure pump. From this, the high pressure pump itself may not need to be modified which could reduce costs associated with retrofitting existing fuel systems. Also, by regulating the two different pressures (such as a high and a low pressure) of the high pressure pump (and fuel rail), the two operating modes may provide a larger range of possible fuel rail pressures more closely aligned with the continuous pressure control of the solenoid activated inlet check valve. Furthermore, since the pressures are regulated via the first and second pressure relief valves, the aforementioned solenoid activated check valve is not necessary and may not be included in the high pressure pump system. Along with the removal of the spill valve, the instructions for controlling the spill valve stored in the controller can be removed, thereby reducing the complexity of the controller. Finally, through mechanical management of fuel pressure via the two pressure relief valves, the overall cost of the fuel system may be reduced, particularly when both port and direct fuel injection are used.
In another example, multiple discrete pressures can be maintained by the high pressure fuel pump instead of only two pressures. By adding additional pressure relief valves and solenoid valves while arranging as discussed below, more than two pressures can be attained by the fuel pump. In this way, fuel systems that require more than two pump pressures and fuel rail pressures in a fuel rail coupled to the direct injectors can be accommodated for. Each of the multiple discrete pressures can be provided by the high pressure pump during certain operating conditions. For example, during engine idling direct injection may not be required, and as such the lower pressure could be provided by the direct injection (high pressure) pump to minimize wear on the various components while still providing lubrication of the pump.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.